Osteoporosis is a pathologic state or disease involving some symptom or risk due to quantitative reduction in bone exceeding a certain degree. Major symptoms are spinal kyphosis, and fractures of dorsolumbar bones, vertebral centra, femoral necks, distal end of radius, ribs, proximal end of humerus, and others. In healthy bone tissue, bone destruction occurs constantly, with a good balance between bone formation and resorption; osteoblasts and osteoclasts play key roles in osteogenesis and bone resorption, respectively. Bone resorption surpassing osteogenesis, upon deterioration of the bone destruction balance therebetween, results in a quantitative reduction in bone. Traditionally, bone resorption inhibitors such as estrogens, calcitonin and bisphosphonates have been mainly used to treat osteoporosis. However, these bone resorption inhibitors fail to have a satisfactory effect in some cases, due to limitation on the subject or to uncertain efficacy. There is therefore a need for a new osteogenesis substance which serves as a prophylactic/therapeutic drug for osteoporosis, to increase once-decreased bone mass.
There are numerous benzopyran derivatives, such as those listed in the overview in the Progress in Medicinal Chemistry, Vol. 9, p. 65 (1973). That publication, however, does not describe the osteogenesis-promoting action of 4-oxo-4H-1-benzopyran-2-carboxamide derivatives. Nor is any such derivative known that has a substitutional group containing phosphonic acid as an N-substituent.
Also, European Patent Publication EP-524023-A1 describes the following compound as a therapeutic agent for osteoporosis. ##STR4##